1. Field of the Invention
The present invention relates to an axial tube assembly for a motor. In particular, the present invention relates to an axial tube assembly for reliably positioning a bearing of a motor. The present invention also relates to a motor having such an axial tube assembly.
2. Description of Related Art
FIGS. 1 and 2 of the drawings illustrate a conventional motor including a casing 10, a bearing 20, a stator 30, a circuit board 31, and a rotor 40. The casing 10 includes an axial tube 11 integrally formed on a central portion of the casing 10. The axial tube 11 includes a stepped portion 11a on an inner periphery thereof and a plurality of longitudinal slits 11b in a top end thereof. The slits 11b allow the axial tube 11 to expand radially outward. After the bearing 20 is mounted into the axial tube 11, a retaining cap 11c is mounted to the stepped portion 11a to improve assembling reliability, and a shaft 41 of the rotor 40 is then extended through the retaining cap 11c and the bearing 20. Further, at least one rib 1d is formed on an outer periphery of the axial tube 11 for engaging with at least one groove 30a in a longitudinal hole of the stator 30 to provide a reliable positioning for the stator 30. Further the stator 30 includes a plurality of legs 30b engaged with the circuit board 30. After assembly, the retaining cap 11c urges the top end of the axial tube 11 to expand radially outward, thereby preventing the stator 30 from being disengaged from the axial tube 11.
The above-mentioned motor has a simple structure that is easy to assemble and that has a low manufacturing cost. However, the assembling reliability of the motor is low, as the retaining cap 11c is the only member for maintaining the positional relationships among the bearing 20, the stator 30, and the circuit board 31. Further, in a case that the axial tube 11 and the bearing 20 have a relatively large tolerance therebetween, the bearing 20 is apt to rotate together with the shaft 41 of the rotor 40. Further, coaxiality of the axial tube 11, the bearing 20, and the shaft 41 of the rotor 40 could not be achieved, as the bearing 20 is directly engaged in the axial tube 11 without any positioning assistance. As a result, the rotational stability is adversely affected, resulting in imbalanced rotation and generation of noise. Further, since there is no means for preventing the retaining cap 11c from being disengaged from the axial tube 11, the shaft 41 might shake and thus cause a retainer ring 20a mounted to a distal end of the shaft 41 to exert an axial force to the bearing 20 and the retaining cap 11c, causing disengagement of the bearing 20 and the retaining cap 11c from the axial tube 11. Further, a relatively large gap exists between the axial tube 11 and the rotor 40 such that dusts in the air current might enter and thus contaminate the lubricating oil in the bearing 20. The speed of the rotor 40 is thus lowered, and the life of the motor is shortened.